In an optical network, Dense Wavelength Division Multiplexing (DWDM) permits the multiplexing of multiple optical carriers onto a single optical fiber by using different wavelengths of laser light. DWDM can carry more optical channels compared to, for example, Coarse Wavelength Division Multiplexing (CWDM). As a result, DWDM is used in optical networks in which denser optical channel spacing is needed.
According to DWDM, each transport channel has only one optical carrier that occupies a fixed optical bandwidth. Since the total usable optical bandwidth of an optical fiber is fixed, a DWDM system has a fixed number of total optical channels. For example, the total usable bandwidth of an optical fiber may be about 5-10 THz. In this instance, a DWDM system can have a fixed number of optical channels, such as a 96-channel system or a 128-channel system. The fixed optical bandwidth also includes bandwidth to separate adjacent optical channels, which is known as channel spacing. For example, 10-Gb/s optical systems may have a channel spacing of 100 GHz or a channel spacing of 50 GHz. Additionally, according to the DWDM system, a central frequency of an optical channel is anchored to a frequency grid defined by a standard body, such as the International Telecommunication Union (ITU).